Whole ratio and part where whole is less than 50

Question

A class includes both sixth graders and seventh graders. The ratio of sixth graders to the total number of students in the class is 3:8. There are 20 seventh graders in the class. How many students in the class?

Answer 1

Because the class is made up only of 6th and 7th grades, and the ratio of 6th grades to total is 3:8, you can infer that the ratio of 7th grades to total is 5:8 (3+5 for the total of 8)

From here, since you know there are 20 7th grades total:

5:8 -> 20:?

5*4 = 20 so...

8*4 = 32

20:32 There are 32 students total.